Why is my foam roof swating? Dew?

About 1 month ago, we had or foam roof recoated (it was 5 years old).
Perhaps the biggest difference between the old surface and the new
surface, is that the old surface had little white granules (some foam
roofers add those) and the new surface does not.

This morning, we noticed a very small amount of water trickling out of
some of our down spouts. I got up on a ladder, and I was surprised to
see that the surface of the roof was slightly wet - and in some cases,
enough water was forming near down spouts, such that water was
trickling down.

I also noticed that our neighbor's roof (about 10 feet away) was
slightly wet, and their roof also had some water trickling over the
sides. (We both have Eichlers, but our roof is flat and their's is
sloped.) They had a new foam roof installed, about a year ago, from
the same company that just recoated our roof (so I'm assuming the
surfaces are very similar).

Is this simply a case of dew forming on the roof? Is there something
about a foam roof that makes it a good surface for dew formation?
Does the lack of the the white granules make it an even better surface
for dew formation? Is this something other than dew?